My serial number starts with vm44
If its first five characters are between VM440 and VM516, it is among those with the logic board problems. The typical problem is capacitors. A number of computer manufacturers in addition to Apple bought capacitors from the same firm. Most were bad, leaking and causing a variety of failures. Programs set up to help users with affected machines have long since expired. So I doubt the damp was an issue in this case, but cool weather and extreme humidity are bad for electronics. Any condensation can lead to a fault.
The usual cure for eMacs with the affected logic boards was a new logic board. However, without the protection of a service program, the cost of repair today could buy you another nicely appointed iPad. Also, so many working logic boards for that model went to service affected models that they are hard to find.
A place in Oregon USA had a service where they took the bad logic boards, reflowed new capacitors and other affected parts and returned your board in working condition. This was great because the charge roughly a fourth of the cost of a logic board replacement. Sadly, they have closed their doors; too good a deal, I suppose.
I have heard that consumer protection laws in the UK are different from my side of the Pond. Some devices are considered warrantable for so many years regardless of what the manufacturer says. Does any of that help you?
I'll check back later today. In spite of an unusually foggy day for our normally dry part of the NW ex-colonies, I have a "hankering" for a walk. Had knee replacement surgery three months ago and I have to keep the new hardware moving! Getting old is not for the faint of heart!
I can't find an ending sequence of OTB either